[0001] This Invention consists of an automatic system for the measurement of flow rate and
monitoring of positive-displacement pumps.
[0002] Existing measurement systems are generally adequate for the measurement of fluids
having at least one constant characteristic. There is no all-purpose flowmeter for
accurate measurement without re-calibration of all of the types of fluids likely to
be handled by a positive-displacement pump. The characteristics of these fluids may
vary widely; they may be highly viscous or fluid, conductors of electricity or not,
have solid particles in suspension or not, be liquid or gaseous etc. Flow may also
be laminar or turbulent. There are many flowmeters suited to the measurement of specific
fluids but none which provides accurate measurement for all of these types of fluid.
This Invention provides for measurement of flow rate of any fluid discharged from
a positive-displacement pump. The nature of the flow, whether laminar or turbulent,
does not affect the accuracy of measurement.
[0003] The Invention makes use of the volumetric pumping characteristics of positive-displacement
pumps. A technique commonly used is to count the number of pump strokes and to multiply
this number by the theoretical volume discharged by one stroke. This method of measurement
remains accurate so long as the pump and pumping conditions remain good.
[0004] However, if either of these conditions deteriorates, such systems may become highly
inaccurate. Consider an extreme case in which the pumping conditions are so bad that
the fluid to be pumped does not even reach the pump. This will not prevent the pump
from running as though conditions were normal. The flowmeter will still indicate a
flow proportional to the speed of the pump even though no fluid is actually discharged.
Such an indication is totally false. This is an extreme example, however conditions
under which the fluid does not entirely fill the chambers during the suction phase
are met frequently. Under these conditions the counting of the number of strokes method
is erroneous as the volume actually pumped is less then the theoretical volume which
should be discharged.
[0005] The Invention uses this technique of counting the number of pump strokes and corrects
it by measuring the volume of fluid actually discharged at each stroke. In this way
correct measurement of the flow rate is obtained regardless of pumping conditions
or the condition of the pump.
[0006] In order to measure the volume of fluid actually discharged by the pump, the operational
state of the hydraulic part of the pump must be known. Constant monitoring of pumping
conditions and operational condition of the pump are provided. In the event of damage
to a valve resulting in a leak or if a valve spring should break, the system will
measure the leak and correct the flow rate value accordingly. To our knowledge there
are no existing systems which monitor by detection and correction for leaks at the
valves or cylinder sleeves: leaks or spring-breaks are usually detected by the operator,
alerted by noise from the pumps or vibrations on the fluid circulation lines. The
system resuslting from this Invention will carry out permanent and automatic monitoring
of such malfunctions.
[0007] Monitoring is performed by the microcomputer. If certain parameters reach or exceed
pre-determined values, the microcomputer will make the required calculations to monitor
correct pump operation. It checks the sensors and then checks over several cycles
that the fault is real. If the fault is confirmed the microcomputer transmits the
data and takes the measurements required for flow correction.
[0008] The data transmitted are generally the values for the flow and the volume of fluid
actually discharged from the pump, as well as a value given by a "
pumping conditions and state-of-pump" indicator. The latter is in fact the volumetric
efficiency of the pump, i.e. the ratio between the volume actually discharged, over
the volume theoretically discharged under perfect pumping conditions with a perfect
pump. This indicator is extremely useful for observing the reactions of the pump to
variations in pumping conditions. The operator of a pump knows in real time if the
pumping conditions have been improved or worsened due to his actions or to external
actions. Valve or sleeve leaks, spring-breaks and sensor malfunctions are also transmitted.
Figure 1 shows an example of connection of the invention system.
Figure 2 is a cross-section through the compression chamber of an example of a positive-displacement
pump (piston pump).
Figure 3 is a working drawing for the construction of the microcomputer.
Figure 4 is a sample of curves obtained from an operating pump with the aid of pressure
and displacement sensors and by calculation.
Figure 5 shows the pressure curves for 2 chambers in a triplex pump and the moment
when the moving parts are at rest.
[0009] (The same numberical references indicate the same part on the various figures).
[0010] In Figure 1, item 1 is a central display and checking unit providing real-time monitoring
of a set of positive-displacement pumps and recording the pumping operations. Items
2 are the local monitoring elements intended for use by the pump operators. Items
3 are microcomputer units, part of the Invention. Depending on their configurations,
these microcomputers can be connected to one or several positive-displacement pumps.
In Figure 1, they are connected successively from left to right to two triplex pumps
4, a quintuplex pump 5 and then to two triplex pumps 4 again. The use of a multipoint
serial data bus between parts 1 and 2 simplifies the addition or removal of a particular
equipment item. A similar bus is used between parts 2 and 3, allowing for connection
of other sensors in series with microcomputer 3, plus the use of a single line to
local monitoring unit 2.
[0011] The number of pressure sensors 6 connected to microcomputer 3 is equal to the sum
of the number of discharge chambers 7 of pumps 4 or 5 to which microcomputer 3 is
connected. The number of proximity sensors 8 is equal to the number of pumps 4 or
5 connected. In other words, there must be a pressure sensor 6 for each discharge
chamber 7 and a proximity sensor 8 per pump 4 or 5.
[0012] A preferential mode for realisation of the Invention consists of sensor 8 detecting
the passage of a ring (B) attached to the piston and providing a position reference.
In a known manner, the nature of the reference willl be selected to suit the sensor;
the preferred example would be a steel ring detected by an inductive proximity sensor
8.
[0013] Another example consists of an optical sensor associated with an optical reference
on the piston or a Hall-effect sensor associated with a reference consisting of a
magnet.
[0014] The pump phase reference can also be obtained, for example, by detecting passage
of a referenced tooth on a piston drive wheel or similar part mechanically linked
to the piston, or by a sensor as described above.
[0015] Figure 2 is the cross-section through a discharge chamber 7 of an example of a positive-displacement
pump 4 or 5. The principal characteristic of positive-displacement pumps 4 or 5 is
that discharge chamber 7 is filled by the alternating action of slide 9, and then
evacuated into discharge circuit 10. The direction of fluid flow is established by
valve 11, known as the suction valve, and valve 12, known as the discharge valve.
Movement of valves 11 and 12 is determined by the action of suction valve spring 13
and discharge valve spring 14, and by the forces exerted by the moving fluid and the
pressures in discharge circuit 10, the discharge chamber and suction circuit 15.&
</PAR>
[0016] The preferred configuration is with pressure sensor 6 mounted on the inner side of
flap P to chamber 7. In this way the sensor does not weaken the pump body. However,
if this solution is technically too complex, the sensor may be installed flush on
another flat part of the chamber.
[0017] Normal pump operation is as follows: when slide 9 advances into discharge chamber
7 from its stationary position (point which corresponds to maximum withdrawal), the
fluid in the chamber is firstly expelled into suction circuit 15 until suction anti-return
valve 11 closes, cutting off the fluid flow.
[0018] The fluid is then compressed into discharge chamber 7 until the forces exerted on
discharge valve 12 by the pressure in chamber 7, become greater than the forces on
this same valve 12 by the pressure in discharge circuit 10 plus spring 14. At this
moment, discharge valve 12 opens and the fluid is expelled into the discharge circuit.
The volume of fluid delivered into discharge circuit 10 is equal to the volume displaced
by slide 9 as the latter advances into chamber 7 from the position it occupied at
the moment discharge valve 12 opened, up to its stationary position corresponding
to maximum penetration into chamber 7.
[0019] For many positive-displacement pumps this calculation is not sufficient: when slide
9 withdraws from discharge chamber 7 from its stationary (maximum-penetration) point,
discharge valve 12 is not necessarily closed, especially when the pump is running
at high speed. A certain volume of fluid therefore flows back into discharge chamber
7 until discharge valve 12 closes. This volume must be deducted from the volume expelled
by the pump into discharge circuit 10; it is equal to the volume displaced by slide
9 when it withdraws from its stationary (maximum-penetration) point in discharge chamber
7, before closure of discharge valve 12.
[0020] Figure 3 is a block diagram of a microcomputer unit. Item 15 is a microprocessor
system with its clock, bus and memories. A safeguarded memory 16 provides for storage
of a certain quantity of data, in particular the calibration values of pumps 4 and
5 which are connected to the microcomputer. These values allow in particular for the
calculation of the volumes displaced by slide 9 betweem its stationary position and
its position at the moments of opening and closing of discharge valve 12. Items 17
are connecting parts providing links with the multipoint serial bus. In addition,
pressure sensors 6 are connected to microcomputer 15 via adapters 18. Similarly, proximity
detectors 8 are connected to microprocessor system 15 by adapters 19. Items 6, 18,
and 19 are sufficient in number to provide for a pressure sensor 6 and an adapter
18 per discharge chamber 7, and for a proximity detector 8 and an adapter 19 per pump
4 or 5.
[0021] Figure 4 shows three curves plotted against time. Curve 21 shows the variations in
the output signal from a discharge sensor which measures the position of discharge
valve 12. At the origin point, valve 12 is at rest on its seat: the curve is at maximum.
As the curve begins to drop this indicates that valve 12 is moving away from its seat.
The fluid then begins to be discharged into the discharge circuit 10.
[0022] Knowing the moment of origin when slide 9 is in the stationary position corresponding
to maximum withdrawal from chamber 7, plus the moment at which valve 12 begins to
leave its seat, it is possible to calculate the volume displaced by slide 9 between
these two moments. Curve 22 represents the signal from a sensor 6 placed in discharge
chamber 7 corresponding to discharge valve 12 whose position is observed. Curve 23
is the derivative in relation to time, of curve 22. Research during development of
the Invention showed that use of the derived curve brought technical improvements.
Part of the Invention consists in using a pressure sensor 6 to detect opening and
closing of discharge valves 12: use of movement sensor is not always suitable for
meas ment of the movement of valve 12 inside the pump, whereas
a pressure sensor has no moving parts and resists the pressures created by the pumps.
Furthermore, pressure sensor 6 gives more information on the operational state of
the pump than would a movement sensor measuring the movement of discharge valve 12.
The highest point of curve 23 corresponds to the exact moment of opening of valve
12: this is used in the software of microcomputer 3 to determine the moment of opening
of valve 12 from the form of the signal representing the pressure in the chamber.
The moment of closing of discharge valve 12 is calculated in a similar way.
[0023] Another technique used to determine the moment of opening and closing of discharge
valves 12 in another configuration of the Invention makes use of the comparison between
the signals from a pressure sensor 6 in discharge chamber 7 and a pressure sensor
of the same type in discharge circuit 10: when the signals are equal, discharge valve
12 is open. If the pressure in the discharge chamber is lower than the pressure in
discharge circuit 10, discharge valve 12 will be closed. Some difficulties are encountered
with this technique as it requires the use of pressure sensors which are sufficiently
accurate to allow for comparison. (The use of correlating algorithms allows for correction
and real-time comparison of the signals from the sensors even where the latter are
not very accurate. However, use of such algorithms may prove to be too long in relation
to the real-time requirements of the application).
[0024] For certain applications, pumping is regular: any changes in the volumetric efficiency
of the pump take place slowly in relation to the operating speed of the pumps plus
the calculations performed by microcomputer 3. In such cases it is often the case
that the volumetric efficiency of the pump does not vary during several pumping cycles.
It is therefore necessary to perform the efficiency calculations every n cycles only,
and to connect several pumps to a given microcomputer 3.
[0025] Microcomputer 3 calculates the volumetric efficiency of each pump in turn. This value
is stored in memory and used as often as necessary, (e.g. every second), along with
the pump operating speed, for flow-rate calculation for each pump (the volumetric
efficiency value being assumed to be constant since it was calculated for the last
time).
[0026] Figure 5 shows signals 24 and 25 from two pressure sensors 6 in two discharge chambers
7. The pressure sensor 6 whose signal is represented by curve 24 is located in a discharge
chamber 7 whose discharge valve 12 is in good working order. On the other hand the
pressure sensor 6 whose signal is represented by curve 25 is in a discharge chamber
7 whose discharge valve 12 is defective so that there is a leak from discharge circuit
10 to discharge chamber 7 when discharge valve 12 is at rest on its seat. The pressure
in discharge circuit 10 is greater than the pressure in suction circuit 15. The vertical
lines represent the moments when the respective discharge chamber slides 9 are stationary.
The Invention is partly based on the observation that whereas curve 24 shows that
the pressure in discharge chamber 7 does not increase before immobilising of slide
9, the pressure in discharge chamber 7 with a faulty discharge valve 12 does increase
before the slide stops.
[0027] An observation of the same type may be made for faults ocurring at intake valves
11, the piston sleeves or for breakage of springs 13 and 14. These observations are
used by the microcomputer 3 software to determine the state of the valves, sleeves
and springs.
[0028] When a leak is detected (and provided the discharge pressure is high enough), it
is possible to measure the quantity of fluid leaked by analysing the development of
the pressure-increase curve in chamber 7.
[0029] When the system is in operation the microcomputer runs a program stored in memory
which contains a number of tasks which may be as listed be
low (but not necessarily in the given order):
- Energizing and initialisation of microprocessor (15).
- Acquisition of data from pressure sensors 6 and proximity detectors 19.
- Calculation of moments of opening and closing of discharge valve 12 of each discharge
chamber 7 by one of the methods indicated above.
- Detection of the state of the pump (running or stopped), and calculation of operating
speed according to the case.
- Calculation of moments of immobilisation of slide 9 of each discharge chamber 7
by analysis of signals from proximity detectors 8.
- Calculation of volumes of fluid actually discharged and volumes re-introduced into
each discharge chamber 7.
- Comparison of values calculated with values determined so as to initiate certain
calculations for checking of condition and correct operation of various (pump) parts,
plus calculation of any leaks.
- Calculation of volumetric efficiency of each pump.
- Calculation of cumulative flow and volume for each pump.
- Transmission of data via data bus.
- In the event of request from a local monitoring unit, running of test programs or
special calibration programs, storing in permanent memory or communication of certain
parameters.
[0030] Microcomputer 3 can perform numerous other calculations and run other programs; those
listed above are given by way of example.
[0031] The system resulting from the Invention is designed to be sufficiently flexible in
application to allow it to be used with different types of positive-displacement pumps.
[0032] Appended Figure 6 represents the display panel for the unit, per the Invention. This
shows more clearly the progress represented by the Invention, since in addition to
accurate and precise measurement of flow and volume, it provides a direct reading
of volumetric efficiency and indicates operating faults. the "Chamber" window equipped
with LEDs indicates the chamber in which the fault has appeared as well as the valve
concerned. This allows an operator to intervene immediately and with maximum effectiveness
which is not possible with presently existing systems.
FIG. 6
[0033]
1. FLOW
2. VOLUMETRIC EFFICIENCY
3. VOLUME
4. CHAMBER
5. MOTOR 1
6. METRIC
7. NO
8. UNITS
9. 1/MIX
10. 2/DIAMETER
11. SUM
12. LOCK
13. MOTOR 2
14. 100 RPM
1) Positive-displacement pump and free valves, characterised by the fact that they
comprise a system for detection of opening and closing of at least one discharge valve
by observation of the pressure in at least one piston discharge chamber and/or pump
discharge circuit, combined with a system for detection of the position of at least
one moving part mechanically linked to piston movement or to such a system.
2) Pump as per Claim 1, characterised by detection of opening and closing of all of
the discharge valves.
3) Pump as per Claim 1 or 2, characterised by detection of opening and closing of
the discharge valve(s) by comparison of the discharge chamber pressure and the pressure
in the pump discharge circuit.
4) Pump as per Claim 1 or 2, characterised by detection of opening and closing of
the discharge valve(s) by observation of the pressures in the discharge chambers.
5) Pump as per any of Claims 1 to 4, characterised by the fact that the detection
system consists of a reference attached to the piston and whose passage is detected
by a suitable detector, e.g. steel ring, induction sensor, optical reference, optical
or magnetic sensor or Hall-effect sensor.
6) Pump as per Claims 1 to 5, characterised by a sensor measuring the pressure in
one piston chamber, the sensor being mounted on the inside of the chamber flap.
7) System for detecting the opening and closing of at least one discharge valve by
observation of pressure in one piston discharge chamber and/or pump discharge circuit,
combined with a position detection system comprising at least one moving part mechanically
linked to piston movement.
8) System as per Claim 7, characterised by detection of opening and closing of all
the discharge valves.
9) System as per Claims 7 or 8, characterised by detection of opening and closing
of a discharge valve or valves by comparison of discharge chamber pressures and pressure
in the pump discharge circuit.
10) System as per Claims 7 or 8, characterised by detection of opening and closing
of the discharge valve(s) by observation of pressures in the discharge chambers.